Mechanisms to control the lowering and closing speed of rolling doors or shutters have been in use for several years. Among the doors controlled by these regulating mechanisms are rolling fire doors, which generally include a curtain of horizontally interconnected slats connected at one end to a rotatable support shaft. Upon winding of the support shaft, the door is raised to its open position. The door is operable to unwind or unroll by the urging of gravity or under motor control to its lowered or closed position.
In operation, rolling fire doors release from their open position during an emergency and close by gravity or in some designs, by motor operation. In the absence of a speed regulating mechanism to control the rotational speed of the support shaft, the speed at which the door descends increases as the door drops, and the door could be damaged upon impacting the floor, thus failing to seal off the door opening. Additionally, a free-falling door could cause serious injury to persons.
Numerous mechanisms are known and have been used for controlling the speed of descent of such doors in a fire or other emergency situation, such as centrifugal brakes, oscillating governors or viscous speed governors attached to the support shaft of the rolling door. These regulating mechanisms differ significantly in their respective application of braking force to the support shaft of the rolling fire doors.
Centrifugal brakes generally consist of a brake drum and a brake shoe. Two tension springs hold the brake shoes in a closed position until the support shaft attached to the centrifugal brake is rotated at or above a preset speed at which point the brake shoes begin to separate due to centrifugal force and thus apply a braking force against the inside of the brake drum to slow the speed of the rotating support shaft.
Oscillating governors generally comprise a gear mechanism coupled to the support shaft and an oscillating ring associated with the door operator. During closing movement of the fire door, the ring is adapted to swing in a back-and-forth motion as it engages teeth of the gear mechanism. The teeth disposed on the ring component intermittently abut the outer surface of the gear, thereby regulating the rate of descent of the rolling door.
Viscous speed governors generally use the shear force of a viscous fluid to retard the rate of descent of rolling fire doors. Typically, a support shaft of the rolling door includes one or more disc-shaped members that are keyed to and rotate with the support shaft. The disc-shaped members rotate within a housing of the viscous speed governor. As the disc-shaped members rotate within the housing, a shear film of a viscous fluid damping medium resists movement of the disc-shaped members relative to the housing. In rolling fire door environments, as the rotational speed of the rotating disc-shaped member within the viscous governor increases, the viscous governor provides a higher damping torque to the support shaft to thereby reduce the rate of descent of the door. The descent rate may be further manipulated by increasing or decreasing the viscosity of the fluid within the governor. The primary operational difference between a viscous speed governor and a centrifugal brake shoe is that the latter provides a somewhat constant braking force once it is actuated, whereas in the former, the damping torque applied increases with an increasing RPM of the support shaft and its associated disc-shaped member of the viscous speed governor.
In rolling fire door environments, several problems are typically associated with the use of centrifugal brakes. For example, the centrifugal brake creates a significant amount of unwanted noise during its operation as a result of the contact between the brake shoe and the brake drum. Additionally, centrifugal brakes provide a generally constant braking force once a certain RPM of the support shaft has been achieved, and the braking does not increase with an increased rotational speed of the support shaft.
Problems are also associated with the use of the oscillating governors in rolling fire door environments, including unwanted noise and the inability to accurately regulate the rate of descent of the door.
In the past, mechanisms to control the rate of descent of rolling fire doors have been connected directly to the support shaft of the door. To control the rate of descent of larger fire doors, multiple speed regulating mechanisms have been attached to the support shaft of the door in a stacked arrangement. In "stacking", multiple braking mechanisms are mounted or associated with the support shaft of the rolling door curtain. "Stacking" results in several known problems, including additional space requirements, additional cost and door size limitations. Often, the fire door is covered by a hood which envelopes the curtain of the door in its raised position and extends along the lintel at the top of the door opening. Generally, this allows very little space in which to place a speed regulation mechanism. As more speed regulating mechanisms are "stacked", the problem of limited space is exacerbated. "Stacking" is also a costly solution as each additional braking unit adds to the cost of the rolling fire door system. Moreover, with "stacking", the maximum door size is limited since the resulting damping torque from the "stacked arrangement" only increases fractionally with each added speed regulating mechanism which limits the use of this approach.
Accordingly, it is desirable to operatively connect a speed regulating mechanism to a rolling fire door in a manner that eliminates the problems of space, door size limitations, and cost associated with stacking of speed regulating mechanisms. It is also desirable to have a speed regulating mechanism which can operate with minimal noise. Likewise, it is desirable to have a speed regulating mechanism which has a reduced potential of seizing or jamming during its use. Finally, it is desirable to have a speed regulating mechanism which is capable of consistently, accurately, and safely regulating the closing speed of rolling fire doors of various sizes.